In orchards, farmers combat harmful pathogens like fungi, which can destroy their crops, using chemical weapons such as fungicides. However, bees are often the victims of collateral damage in this perennial battle. Some fungicides affect the amount of energy organisms can produce. Ling-Hsiu Liao and colleagues from the University of Illinois at Champagne-Urbana, USA, had a hunch that if honeybees consumed fungicide, they might produce less energy in the muscles that they use for flying and their flight performance could suffer.
The team recently built a honeybee treadmill, in which the insects are tethered while flying, to investigate how a fungicide, boscalid, affects their flight. The bees wore tiny iron plates so that they could be carefully attached to a magnetic rod while flying. In addition to furnishing their treadmill with tiny televisions that tricked the bees’ eyes into thinking that they are moving forwards, the researchers installed fans blowing on the bees to dupe them into thinking that they were flying freely.
To investigate the effects of the fungicide on flight, the researchers supplemented the pollen diet of a colony of honeybees with boscalid-laced sugar water. Then, they selected bees that were keen to fly outside of the hive and set the insects flying on the treadmill. The fungicide-fed bees beat their wings together at a lower frequency than bees that did not have a fungicide-supplemented diet. As wingbeat frequency affects flight speed in other insects, it seems likely that fungicides make honeybees slower, affecting their ability to find food quickly before running out of energy.
While this might seem like grim news for honeybees, the researchers had an idea that a natural chemical in bee food could ameliorate these effects. They wondered whether quercetin, which occurs naturally in pollen, could increase the amount of available energy that bees have for flying. The researchers raised another colony of bees fed a quercetin-rich diet. They then measured the chemical that bees use to power flight – adenosine triphosphate (ATP) – in the insects’ flight muscles and found that the bees that had been fed quercetin had much more ATP than those that had not received a quercetin supplement. This suggests that quercetin in bee food increases the amount of energy bees have for flying, which could help them fly faster or longer, to offset the negative effects of the fungicide.
To test this theory directly, the researchers took honeybees from another colony that had been fed on quercetin and the fungicide and put them through their treadmill test. As predicted, bees fed on the two chemicals had a wing beat frequency very similar to that of bees that had not had their diet supplemented, supporting the researchers’ theory that quercetin in bee food remedies the impact of the fungicide on flight.
While quercetin seems to relieve the negative effects of fungicides on honeybee flight, other species may not be so fortunate. Liao's treadmill could hopefully help scientists understand the negative effects of pest control on other pollinators and inform future conservation efforts to protect those species.